Fish are facing new kinds of threats — but there's hopeBack to video

Nobody was thinking as much about these topics back in 2006, when an ecologist named David Dudgeon published the authoritative overview of the world’s fresh waters. Thousands of scientists have built their own research on that work in the past dozen years.

“I spent all of my undergrad and my masters referencing this (Dudgeon’s) paper, and it was just becoming outdated,” said Andrea Reid, who is doing her PhD in biology at Carleton University.

Reid decided it was time for an update, and that work (with Dudgeon and others teaming up) is now published in a journal called Biological Reviews.

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“A lot of the threats are still present, but so many news ones have emerged,” she said in an interview.

Hydroelectric power is one. Dams have been blocking rivers to create electricity for decades, accidentally preventing fish from migrating up and down as they hatch, mature and return to spawn. While North Americans have removed some dams, Reid said “there are now 3,700 major hydro power dams that are either planned or under construction,” many in South America and India.

The use of dot-sized microplastics has expanded since the overview written back in 2006.

And while chemical pollutants have been in water for a long time, “We’re seeing there is definitely a shift (in chemicals),” said Reid. “We are seeing a lot of pharmaceuticals in water, like antibiotics that are accumulating in the river systems and are going without treatment.”

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Sewage treatment plants are built to remove solids and kill germs, not to remove antibiotics. People flush unused pills down the toilet, or excrete them in urine, and fish absorb them.

“For the most part, they get into the ecosystem undetected,” she said. They can cause fish and other animals in the water to have fewer or less healthy offspring.

From other pollutants, there are “a range of impacts (on fish) ranging from reduced abundance of fish to effects on individual fish,” such as “inter-sex fish … that are essentially stuck between two sexes.”

Many of these effects occur downstream from cities.

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“A lot of people aren’t even aware of these problems. They kind of go unnoticed,” Reid said. “They are happening under the water’s surface and there aren’t the same cheerleaders for these lesser-known fish as there are for the killer whales off the coast, or seals. They really do get forgotten.”

But her work also found sources of hope.

For instance, an upgrade to the sewage plant in Kitchener-Waterloo has been able to remove many pharmaceuticals. “They are now finding fewer inter-sex fish in the Grand (River),” said Steven Cooke, a Carleton biology professor who is Reid’s supervisor.

Another useful tool is environmental DNA, or eDNA. This refers to the genetic traces that animals leave behind them in water or on land — for instance by sloughing off bits of skin or scales, or in droppings.

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“We can monitor things on a huge scale. We can monitor an entire drainage basin and know what’s in the fresh water and in the terrestrial habitat,” Reid said.

“As a good example, a colleague of mine is monitoring eDNA in Kruger National Park in South Africa.” He takes samples at watering holes, and learns how species interact there.

This monitoring in turn makes solid information available to governments and regulators so they can design conservation measures that fit the need.

This overview of issues “will keep the alarm bells ringing,” Cooke said. “We need to keep looking forward instead of being reactive. … But within all of this there is also some optimism, I think. People do care, (and) there are some advances in water treatment.

“But some of these (conservation measures) are not engineering changes. They are about wholesale changes in human behaviour.”

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